Java Streams: find if stream contains null

Question

Most probably a duplicate, however I was not able to find any particular one.

Given

public static void main(String[] args) {
    System.out.println(
            Arrays.asList(null, null, 1)
                    .stream()
                    .filter(obj -> obj == null)
                    .findAny()
                    .isPresent()
    );
}

Expectation

Should at least work (i.e return false because findAny returns Optional).

Actual

NullPointerException is thrown

Question

Is it a bug or a feature?

Thanks for your opinion and explanation.

see my revised answer

syntagma
– syntagma

2017-06-01 18:59:14 +00:00
Commented Jun 1, 2017 at 18:59 — syntagma
– syntagma, Commented Jun 1, 2017 at 18:59

fps · Accepted Answer · 2024-09-17 18:41:08Z

17

If you change your code to use anyMatch instead of filter(...).findAny().isPresent(), it works as expected:

boolean found = Arrays.asList(null, null, 1)
        .stream()
        .anyMatch(Objects::isNull);

System.out.println(found); // true

As to why your version fails with NPE, in the Stream.findAny docs it says:

Throws:

NullPointerException - if the element selected is null

So this is expected behavior.

EDIT: The NPE occurs because Optional.of is used to construct the value returned by findAny(). And Optional.of requires a non-null value, as per the docs:

Returns an Optional with the specified present non-null value.

Anyways, I suppose you'd like to know why Optional.of was used instead of Optional.ofNullable, when building the value returned by findAny()...

Well, I can only speculate, but I think that findAny() and findFirst() are meant to find values that match some criteria, i.e. a Person whose name starts with A. It can be the case that you want to know whether there's a null element in your stream. But, in this case, you don't need to actually find such element, because you already know that, if you find it, it will be, well... just null. So it's enough to only check if your stream contains null, and you can perfectly use anyMatch() to find if that's the case.

In other words, it wouldn't be of much use to find an element that is null, because you can't do anything with it (apart from knowing that it's null).

EDIT 2: As user @holi-java indicates in his comment below, if findAny() returned Optional.ofNullable(null), then there would be no way to know whether null was found or not. In this case, the result would be ambiguous, because Optional.ofNullable(null).equals(Optional.empty()) == true, i.e. it would result in confusion, since Optional.ofNullable(null).isPresent() == false, meaning there was no matching value found.

edited Sep 17, 2024 at 18:41

answered Jun 1, 2017 at 18:42

fps

34.5k8 gold badges62 silver badges116 bronze badges

Sign up to request clarification or add additional context in comments.

15 Comments

holi-java Over a year ago

well, good job. It is another time difference to submit, ^_^.

holi-java Over a year ago

a Optional has 2 states: absent & present. if findAny using Optional.ofNullable then it has 3 states: absent & null & present. if we want to distinct between absent and null, then we must compare with optional == Optional.empty() , and then we back to checking an object whether is null as object == null and Optional loses it role for avoid checking nulls, and can't chain a Optional with 3 states as further.

fps Over a year ago

@holi-java maybe it was me that misunderstood you... I'm thinking it as follows: if findAny used Optional.ofNullable to return the found value, and if that found value was null, then you wouldn't be able to know if the value was found or not, because an Optional that has a null value is an empty Optional.

fps Over a year ago

@holi-java my point is that you don't need three states with findAny, you only need two: found and not_found. For the very special case when you want to know if your stream has a null element, use anyMatch

Holger Over a year ago

@Federico Peralta Schaffner: well, in principle, the search condition could include null as possible result, instead of being a search for exactly null. However, this can be considered a rare corner case. I never had a need for this. Besides that, if I want to know whether a list contains null, I’d use list.contains(null) instead of using the stream API…

|

Community · Accepted Answer · 2020-06-20 09:12:55Z

14

This behavior is highlighted in the Javadoc for findAny() https://docs.oracle.com/javase/8/docs/api/java/util/stream/Stream.html#findAny--

Returns:an Optional describing some element of this stream, or an empty Optional if the stream is empty

Throws:NullPointerException - if the element selected is null

Since you are filtering so the Stream only contains nulls, you are getting a NullPointerException as expected.

edited Jun 20, 2020 at 9:12

CommunityBot

11 silver badge

answered Jun 1, 2017 at 18:44

GAdams

2661 silver badge5 bronze badges

Comments

Darshan Mehta · Accepted Answer · 2017-06-01 18:47:53Z

3

Here's the documentation of findAny(), this is what it says:

Throws: NullPointerException -

if the element selected is null

So, you will always get an NPE if you try to invoke findAny() on a null object.

You can use anyMatch instead, e.g.:

Arrays.asList(null, null, 1).stream().anyMatch(e -> e == null));

answered Jun 1, 2017 at 18:47

Darshan Mehta

31k14 gold badges75 silver badges111 bronze badges

Comments

syntagma · Accepted Answer · 2017-06-01 18:58:26Z

It is not a bug, it is a result of calling get() on an instance of Optional which throws NPE. The exact call that causes it is findAny(), which gives the following stack trace:

Exception in thread "main" java.lang.NullPointerException
    at java.util.Objects.requireNonNull(Objects.java:203)
    at java.util.Optional.<init>(Optional.java:96)
    at java.util.Optional.of(Optional.java:108)
    at java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:193)
    at java.util.stream.FindOps$FindSink$OfRef.get(FindOps.java:190)
    at java.util.stream.FindOps$FindOp.evaluateSequential(FindOps.java:152)
    at java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)
    at java.util.stream.ReferencePipeline.findAny(ReferencePipeline.java:469)
    at StreamTest.main(StreamTest.java:17)

Also the documentation for findAny() specifies that NPE can be thrown:

Throws:NullPointerException - if the element selected is null

You can achieve the expected result using anyMatch():

Arrays.asList(null, null, 1).stream().anyMatch(obj -> obj == null)

Why `ofNullable()` was not used in the implementation of `findAny()`?

Designers of the API did not want to assume whether null means the value is not present (absent value) or is present but equals null. Also, you can still use map(Optional::isNullable) on any stream.

Collectives™ on Stack Overflow

Java Streams: find if stream contains null

Given

Expectation

Actual

Question

4 Answers 4

15 Comments

Comments

Comments

Why `ofNullable()` was not used in the implementation of `findAny()`?

Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

Given

Expectation

Actual

Question

4 Answers 4

15 Comments

Comments

Comments

Why ofNullable() was not used in the implementation of findAny()?

Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related

Why `ofNullable()` was not used in the implementation of `findAny()`?